Taste is one of the least understood senses from the biochemical standpoint. Sweet taste can be elicited to varying degrees by a wide variety of compounds such as mono- and di-saccharides, several amino acids and dipeptides, glycerol, cyclamates, and saccharin, as well as some hydrate inorganic compounds. There is no apparent common structural feature among them. Monellin is a protein belonging to a totally new class of sweet compounds. Monellin is about 10,000 times sweeter than sucrose on a molar basis, and required native protein conformation to elicit sweet taste. Our overall objective is to determine three-dimensional structure of this protein and other taste-active compounds to understand the structure-taste relationship of this class of sweet molecules by X-ray crystallographic method. Structural information obtained may help design other compounds having beneficial pharmacological properties for diabetic patients.